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<chapter id='intro'>
<title>Introduction</title>

<section id='intro-welcome'>
    <title>Introduction</title>

    <para>
        This manual provides reference information for the current release of the Yocto Project.
        The Yocto Project is an open-source collaboration project focused on embedded Linux
        developers.
        Amongst other things, the Yocto Project uses the OpenEmbedded build system, which
        is based on the Poky project, to construct complete Linux images.
        You can find complete introductory and getting started information on the Yocto Project
        by reading the
        <ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>.
        For task-based information using the Yocto Project, see the
        <ulink url='&YOCTO_DOCS_DEV_URL;'>Yocto Project Development Manual</ulink>
        and the <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;'>Yocto Project Linux Kernel Development Manual</ulink>.
        For Board Support Package (BSP) structure information, see the
        <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
        You can also find lots of Yocto Project information on the
        <ulink url="&YOCTO_HOME_URL;">Yocto Project website</ulink>.
    </para>
</section>

<section id='intro-manualoverview'>
    <title>Documentation Overview</title>
    <para>
        This reference manual consists of the following:
        <itemizedlist>
            <listitem><para><emphasis>
                <link linkend='usingpoky'>Using the Yocto Project</link>:</emphasis>
                Provides an overview of the components that make up the Yocto Project
                followed by information about debugging images created in the Yocto Project.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='technical-details'>Technical Details</link>:</emphasis>
                Describes fundamental Yocto Project components as well as an explanation
                behind how the Yocto Project uses shared state (sstate) cache to speed build time.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-structure'>Directory Structure</link>:</emphasis>
                Describes the
                <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink> created
                either by unpacking a released Yocto Project tarball on your host development system,
                or by cloning the upstream
                <ulink url='&YOCTO_DOCS_DEV_URL;#poky'>Poky</ulink> Git repository.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-bitbake'>BitBake</link>:</emphasis>
                Provides an overview of the BitBake tool and its role within
                the Yocto Project.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-classes'>Classes</link>:</emphasis>
                Describes the classes used in the Yocto Project.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-images'>Images</link>:</emphasis>
                Describes the standard images that the Yocto Project supports.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-features'>Features</link>:</emphasis>
                Describes mechanisms for creating distribution, machine, and image
                features during the build process using the OpenEmbedded build system.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-variables-glos'>Variables Glossary</link>:</emphasis>
                Presents most variables used by the OpenEmbedded build system, which
                uses BitBake.
                Entries describe the function of the variable and how to apply them.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-varlocality'>Variable Context</link>:</emphasis>
                Provides variable locality or context.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='faq'>FAQ</link>:</emphasis>
                Provides answers for commonly asked questions in the Yocto Project
                development environment.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='resources'>Contributing to the Yocto Project</link>:</emphasis>
                Provides guidance on how you can contribute back to the Yocto
                Project.</para></listitem>
        </itemizedlist>
    </para>
</section>


<section id='intro-requirements'>
<title>System Requirements</title>
    <para>
        For general Yocto Project system requirements, see the
        "<ulink url='&YOCTO_DOCS_QS_URL;#yp-resources'>What You Need and How You Get It</ulink>" section
        in the Yocto Project Quick Start.
        The remainder of this section provides details on system requirements
        not covered in the Yocto Project Quick Start.
    </para>

    <section id='detailed-supported-distros'>
        <title>Supported Linux Distributions</title>

        <para>
            Currently, the Yocto Project is supported on the following
            distributions:
            <note>
                <para>
                    Yocto Project releases are tested against the stable Linux
                    distributions in the following list.
                    The Yocto Project should work on other distributions but
                    validation is not performed against them.
                </para>

                <para>
                    In particular, the Yocto Project does not support
                    and currently has no plans to support
                    rolling-releases or development distributions due to their
                    constantly changing nature.
                    We welcome patches and bug reports, but keep in mind that
                    our priority is on the supported platforms listed below.
                </para>

                <para>
                    If you encounter problems, please go to
                    <ulink url='&YOCTO_BUGZILLA_URL;'>Yocto Project Bugzilla</ulink>
                    and submit a bug.
                    We are interested in hearing about your experience.
                </para>
            </note>
            <itemizedlist>
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                <listitem><para>Ubuntu 12.04 (LTS)</para></listitem>
                <listitem><para>Ubuntu 12.10</para></listitem>
                <listitem><para>Ubuntu 13.04</para></listitem>
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                <listitem><para>Fedora 17 (Spherical)</para></listitem> -->
                <listitem><para>Fedora release 18 (Spherical Cow)</para></listitem>
                <listitem><para>Fedora release 19 (Schrödinger's Cat)</para></listitem>
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                <listitem><para>CentOS release 5.7 (Final)</para></listitem>
                <listitem><para>CentOS release 5.8 (Final)</para></listitem>
                <listitem><para>CentOS release 6.3 (Final)</para></listitem> -->
                <listitem><para>CentOS release 6.4</para></listitem>
<!--                <listitem><para>Debian GNU/Linux 6.0 (Squeeze)</para></listitem> -->
                <listitem><para>Debian GNU/Linux 6.0.7 (Squeeze)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.0 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.1 (Wheezy)</para></listitem>
<!--                <listitem><para>openSUSE 11.4</para></listitem>
                <listitem><para>openSUSE 12.1</para></listitem> -->
                <listitem><para>openSUSE 12.2</para></listitem>
                <listitem><para>openSUSE 12.3</para></listitem>
            </itemizedlist>
        </para>

        <note>
            While the Yocto Project Team attempts to ensure all Yocto Project
            releases are one hundred percent compatible with each officially
            supported Linux distribution, instances might exist where you
            encounter a problem while using the Yocto Project on a specific
            distribution.
            For example, the CentOS 6.4 distribution does not include the
            Gtk+ 2.20.0 and PyGtk 2.21.0 (or higher) packages, which are
            required to run
            <ulink url='&YOCTO_HOME_URL;/tools-resources/projects/hob'>Hob</ulink>.
        </note>
    </section>

    <section id='required-packages-for-the-host-development-system'>
    <title>Required Packages for the Host Development System</title>

        <para>
            The list of packages you need on the host development system can
            be large when covering all build scenarios using the Yocto Project.
            This section provides required packages according to
            Linux distribution and function.
        </para>

        <section id='ubuntu-packages'>
            <title>Ubuntu and Debian</title>

            <para>
                The following list shows the required packages by function
                given a supported Ubuntu or Debian Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image on a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo apt-get install &UBUNTU_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical Extras:</emphasis>
                        Packages recommended if the host system has graphics support:
                        <literallayout class='monospaced'>
     $ sudo apt-get install libsdl1.2-dev xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo apt-get install make xsltproc docbook-utils fop dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo apt-get install autoconf automake libtool libglib2.0-dev
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='fedora-packages'>
            <title>Fedora Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported Fedora Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo yum install &FEDORA_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical Extras:</emphasis>
                        Packages recommended if the host system has graphics support:
                        <literallayout class='monospaced'>
     $ sudo yum install SDL-devel xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
     docbook-dtds docbook-utils fop libxslt dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo yum install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='opensuse-packages'>
            <title>openSUSE Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported openSUSE Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo zypper install &OPENSUSE_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical Extras:</emphasis>
                        Packages recommended if the host system has graphics support:
                        <literallayout class='monospaced'>
     $ sudo zypper install libSDL-devel xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo zypper install make fop xsltproc dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo zypper install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='centos-packages'>
            <title>CentOS Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported CentOS Linux distribution:
                <note>Depending on the CentOS version you are using, other requirements
                    and dependencies might exist.
                    For details, you should look at the CentOS sections on the
                    <ulink url='https://wiki.yoctoproject.org/wiki/Poky/GettingStarted/Dependencies'>Poky/GettingStarted/Dependencies</ulink>
                    wiki page.
                </note>
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo yum install &CENTOS_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical Extras:</emphasis>
                        Packages recommended if the host system has graphics support:
                        <literallayout class='monospaced'>
     $ sudo yum install SDL-devel xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
     docbook-dtds docbook-utils fop libxslt dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo yum install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='required-git-tar-and-python-versions'>
        <title>Required Git, tar, and Python Versions</title>

        <para>
            In order to use the build system, your host development system
            must meet the following version requirements for Git, tar, and
            Python:
            <itemizedlist>
                <listitem><para>Git 1.7.5 or greater</para></listitem>
                <listitem><para>tar 1.24 or greater</para></listitem>
                <listitem><para>Python 2.7.3 or greater not including
                    Python 3.x, which is not supported.</para></listitem>
            </itemizedlist>
        </para>

        <para>
            If your host development system does not meet all these requirements,
            you can resolve this by either downloading a pre-built tarball
            containing these tools, or building such a tarball on another
            system.
            Regardless of the method, once you have the tarball, you simply
            install it somewhere on your system, such as a directory in your
            home directory, and then source the environment script provided,
            which adds the tools into <filename>PATH</filename> and sets
            any other environment variables required to run the tools.
            Doing so gives you working versions of Git, tar, Python and
            <filename>chrpath</filename>.
        </para>

        <para>
            If downloading a pre-built tarball, locate the
            <filename>*.sh</filename> at
            <ulink url='&YOCTO_DL_URL;/releases/yocto/yocto-&DISTRO;/buildtools/'></ulink>.
        </para>

        <para>
            If building your own tarball, do so using this command:
            <literallayout class='monospaced'>
     $ bitbake buildtools-tarball
            </literallayout>
            <note>
                The <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>
                variable determines whether you build tools for a 32-bit
                or 64-bit system.
            </note>
            Once the build completes, you can find the file that installs
            the tools in the <filename>tmp/deploy/sdk</filename> subdirectory
            of the
            <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
            The file used to install the tarball has the string "buildtools"
            in the name.
        </para>

        <para>
            After you have either built the tarball or downloaded it, you need
            to install it.
            Install the tools by executing the <filename>*.sh</filename> file.
            During execution, a prompt appears that allows you to choose the
            installation directory.
            For example, you could choose the following:
            <literallayout class='monospaced'>
     /home/your-username/sdk
            </literallayout>
        </para>

        <para>
            The final step before you can actually use the tools is to source
            the tools environment with a command like the following:
            <literallayout class='monospaced'>
     $ source /home/your-username/sdk/environment-setup-i586-poky-linux
            </literallayout>
            Of course, you need to supply your installation directory and be
            sure to use the right file (i.e. i585 or x86-64).
        </para>
    </section>
</section>

<section id='intro-getit'>
    <title>Obtaining the Yocto Project</title>
    <para>
        The Yocto Project development team makes the Yocto Project available through a number
        of methods:
        <itemizedlist>
            <listitem><para><emphasis>Source Repositories:</emphasis>
                Working from a copy of the upstream
                <filename>poky</filename> repository is the
                preferred method for obtaining and using a Yocto Project
                release.
                You can view the Yocto Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
                In particular, you can find the
                <filename>poky</filename> repository at
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/poky/'></ulink>.
                </para></listitem>
            <listitem><para><emphasis>Releases:</emphasis> Stable, tested
                releases are available as tarballs through
                <ulink url='&YOCTO_DL_URL;/releases/yocto/'/>.</para></listitem>
            <listitem><para><emphasis>Nightly Builds:</emphasis> These
                tarball releases are available at
                <ulink url='http://autobuilder.yoctoproject.org/nightly'/>.
                These builds include Yocto Project releases, meta-toolchain
                tarball installation scripts, and experimental builds.
                </para></listitem>
            <listitem><para><emphasis>Yocto Project Website:</emphasis> You can
                find tarball releases of the Yocto Project and supported BSPs
                at the
                <ulink url='&YOCTO_HOME_URL;'>Yocto Project website</ulink>.
                Along with these downloads, you can find lots of other
                information at this site.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='intro-getit-dev'>
    <title>Development Checkouts</title>
    <para>
        Development using the Yocto Project requires a local
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        You can set up the Source Directory by cloning a copy of the upstream
        <ulink url='&YOCTO_DOCS_DEV_URL;#poky'>poky</ulink> Git repository.
        For information on how to do this, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#getting-setup'>Getting Set Up</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

</chapter>
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